This invention relates to a communication switching system. More particularly, it relates to an improved arrangement and method for the localized self control of randomly allotted time slots or channels to audio ports in a time division multiplexed communication switching system.
In time-shared communication switching systems, such as time division multiplexed (TDM) and pulse code modulation (PCM) systems, it is often desirable to concentrate a large number of audio ports into a fixed number of time slots or channels. Audio ports, in this case, refer to subscriber lines, trunks, tones, etc. Concentrating the audio ports in this fashion results in a highly efficient usage of the time-shared medium.
Normally, in typical time-shared systems, the audio ports are dedicated on a time slot basis, i.e., each audio port is rigidly pre-assigned a hard-wired fixed time slot. There, therefore, must be provided as many time slots as there are audio ports. Such schemes provide 100 percent channel availability, however, a substantial amount of hardware is required. With many types of telephone communication switching systems, this hardware is used very often inefficiently, due to the nature of the telephone traffic. In such systems, the audio ports are individually turned on and off by dedicated leads wired to a central location or common control. Efforts at concentrating these dedicated leads have resulted in complex control circuitry, and hence have been generally undesirable. As a result, numerous problems arise, including among others, the fact that switching transients in the background are increased due to a number of audio ports being given turn on and turn off signals at very rapid rates. Further still, the channel control pulses become of uneven durations, and usually only one audio port can be turned on in any time slot from one decoder.